Comparing flower biology in five species of Gagea (Liliaceae) from southern Italy

The reproductive traits in Gagea are affected by both abiotic and biotic environmental factors. However, further intrinsic drivers, like the ploidy level, could also have a significant influence on the sexual efficiency of these geophytes. Here, we present a comparative study involving the reproductive biology of five species of Gagea occurring in southern Italy, and representing different ploidy levels. The experimental investigations included flower phenology, pollen quality (i.e., morphology, viability, and germination), and stigma receptivity. Such data were then combined with information on seed-set available from previous work. All the studied species showed a gradual pollen presentation, and an early and durable stigma receptivity. Such traits represent effective functional adaptations to prevent pollen limitation under the unpredictable weather dynamics typical of the early blooming season of these plants. The use of a diluted substrate favoured the rate of pollen germination in vitro and, likely, it represents a further adaptation versus adverse environmental conditions (i.e., rain damage on exposed pollen). However, the rates of pollen viability and germination were generally low and appeared related to the ploidy level. Data inherent pollen quality (i.e. morphology, viability and germination) and seed-set indicated the hexaploid G. lutea as the most fertile species, while the heptaploid G. fragifera had the lowest scores for all the considered traits. Finally, by considering the isolation and reduced size of the studied population, the unexpected low fertility found in the diploid G. minima was possibly due to inbreeding depression related to the relict status of this species in southern Italy.